Method and apparatus for preventing unnecessary retransmission of messages in a networked messaging system

ABSTRACT

An improved apparatus and method for routing of messages in a networked system wherein reduced unnecessary retransmission of messages across routers is achieved by examining the address of the source of messages to be forwarded and, if the source of the message is on the transmit side of the router, not retransmitting the message. Further, when messages are originated which do not include source subnet address information, a router receiving such a message will update the source subnet address field of the message with its own source subnet address so as to allow other routers to use the updated source subnet address information in making routing decisions.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to the field of systems for distributedcomputing, communication and control and, more specifically, to the areaof communication of information between devices in a distributedcomputing environment.

2. DESCRIPTION OF THE RELATED ART

There are a large number of networks known in the art which networksallow for communication of messages between nodes that make up thenetworks. In such networks, a node may transmit a message (referred toherein alternatively as the "transmitting node", the "origin node", orthe "source node"). The message may be received by another node (wherethe other node is not the intended final destination node of themessage). This node will be referred to herein as an "intermediate node"and, sometimes, more specifically, is referred to as a "router node".The intermediate node then retransmits the message. This process ofreceiving and retransmitting the message may continue through one ormore additional intermediate nodes until, finally, the message reachesthe final intended destination node or nodes (referred to herein as the"destination node").

Of course, in such a system, designs must provide for retransmission ofthe message until it reaches the desired destination node(s). However,it is important in such designs that the message is not repeatablyretransmitted throughout the network after the message is finallyreceived by the destination node(s) because such retransmission willincrease, unnecessarily, traffic on the network. In fact, as will beseen, in certain scenarios, it is possible for such retransmission tocontinue infinitely until the network is reset.

The present invention offers an improved method of communicatingmessages between nodes in such a network which provides for reducedunnecessary retransmission of messages from node-to-node within thenetwork. In order to describe problems solved by the present invention,it may be useful to refer to FIG. 1.

In FIG. 1, a network is illustrated having 18 nodes referred to withreference numerals 110-128. In this network, nodes 110-114 are membersof subnet 1 102 of domain 1 131. Nodes 116-119 are members of subnet 2103 of domain 1 131. Nodes 120-124 are members of subnet 2 103 of domain2 132 and nodes 125-128 are members of subnet 1 104 of domain 2 132.Nodes 114, 116, 119, 122, and 125 are each router nodes which providefor routing of messages between nodes in different subnets. As will beexplained in greater detail below, nodes may include in transmittedmessages their node id (source node id), subnet (source subnet), anddomain (source domain) and, in the case of group messages, a destinationgroup id.

It is first useful to assume for a first example that nodes 110, 111 and118 are each members of the same group (i.e., group 1). FIG. 2(a)illustrates a prior art method of transmitting a group message from node110 to other nodes in the group (e.g., nodes 111 and 118). Initially,node 110 may format a message and transmit on media 161, block 201. Themessage is received and processed by node 111, block 202. (Nodes 112 and113 may also sense the message but reject it because it is addresses agroup 1.) Node 114 also receives the message, block 203. Node 114 is arouter node and, therefore, accepts the message even though it is not amember of the group designated by the message. Node 114 then transmitsthe message, for example, by RF signals, block 114. In the describednetwork, the message should be received by node 119, block 206 so thatit might be retransmitted on media 155 for reception by node 118 (thethird node in group 1). As illustrated, the message is received by node119, block 206, and is retransmitted on power line 155, block 208, sothat it is received by node 118, block 210. (The message retransmittedby node 119 is also received by node 116 which may retransmit themessage. This will be explained in greater detail below. In addition,the message is received by node 117, however, because this node is notin group 1, the message is ignored. Finally, the message is received bynodes 125-28 which also ignore the message because these nodes are notmembers of domain 1 131.)

Importantly, the message retransmitted from node 114 may also bereceived by node 116, block 205 (and by nodes 122 and 125, block 207).If received by node 116, the message will be retransmitted on power line155 by node 116, block 209. It will be again received by node 118 (andpreferably ignored as a duplicate) as well be being received by nodes117 and 126-128. However, it will also be received by node 119, block211, which will retransmit the message, block 212. The message,retransmitted by node 119 may again be received by node 116 and aseemingly infinite loop is then created. (Of course, the message mayalso be rereceived by node 114, creating similar problems.) If themessage is received by nodes 122 or 125, it will be ignored becausenodes 122 and 125 are not members of domain 1 131.

Many networked computing systems have avoided dealing with theabove-described problem. For example, certain networks only allowtransmission over wire media. This provides for control over recipientsof messages. Other systems implement a "hop count" which is transmittedwith the message. Each time the message is received by a router node,the hop count is incremented and, when it exceeds a predeterminedmaximum, the message is no longer retransmitted by the router nodes. Ofcourse, neither of these solutions is ideal.

Therefore, what is required is a system in which messages areretransmitted in such a manner that the message is received by eachintended recipient but also such that unnecessary retransmission of themessage is not required. Such a system should be media independent.

A second class of problems may also be described with reference to FIG.1 and, now, with reference to FIG. 2(b). Assume in this example, thatnode 110 is unconfigured (an "unconfigured node" as that term is usedherein has not yet been assigned a domain and subnet address and istherefore unable to transmit source domain and subnet information withmessages). In the system of the preferred embodiment, node 110 mayformat and broadcast a message before it has been configured-forexample, node 110 may be requested to transmit its node id onto thenetwork. However, without source domain or source subnet addressinformation, there is no information in the packet to tell the routershow to route the packet.

In the preferred embodiment, node 110 may be requested to transmit itsnode id by activating a "service pin" which is a hardware pin on node110 specially designated to cause transmission of a message whichbroadcasts the node's node id. It is worthwhile to briefly note that inthe system of the preferred embodiment, all nodes are assigned unique48-bit node ids at the time of their manufacture; therefore, even anunconfigured node has a node id. This assignment of unique 48-bit nodeids is better described with reference to U.S. Pat. No. 4,918,690Markkula Jr. et al. titled "Network and Intelligent Cell for ProvidingSensing, Bidirectional Communications and Control" which patent isassigned to the assignee of the present invention.

The message broadcast by node 110 is received by nodes 111 and 112,block 222. The message is also received by node 114, block 223, andretransmitted, block 224. The message may then be received by any or allof nodes 119, block 226, node 116, block 225, or nodes 122 and 125,block 227. Whether or not each of these nodes received the transmittedmessage depends on a number of factors including the strength of thesignal transmitted by node 114 and the capability of each of nodes 119,122 and 125 to receive messages. However, the networked computing systemshould be designed to operate properly in the event any of these nodesreceives the message.

The example of FIG. 2(b) illustrates further detail of the communicationprocess after the message is received by nodes 119 and 116. In the caseof a message received by node 119, block 226, node 119 may retransmitthe message on power line 155, block 228, and it will be received bynodes 116-118 and 125-128, block 230. Node 116 may then retransmit themessage, block 233 and it may then be again received by node 119 (amongother possible nodes). This, of course, creates a potentially infiniteloop of retransmission. The message being received by node 116, block225, creates similar problems wherein node 116 retransmits on power line155 and node 119 (among others) receives the message, block 231, andretransmits, block 232, again creating a potentially infinite loop. (Itmight be noted that preferably nodes 125-128 will ignore the messagebecause they are not members of the proper domain).

Again, what is desired is to develop a system in which unnecessaryretransmission of messages (and especially potentially infinite loops)are reduced, avoided or eliminated.

These and other objects of the present invention will be betterunderstood with reference to the Detailed Description of the PreferredEmbodiment, the accompanying drawings, and the claims.

SUMMARY OF THE INVENTION

A method and apparatus for reducing and preventing the unnecessary andunwanted retransmission of messages in a networked messaging system isdescribed. In the present invention, a network may comprise a first nodecapable of at least communicating information, a second node capable ofreceiving the communicated information, and a third node for receivingthe communicated information from the first node and routing thecommunicated information to the second node. The first and second nodesmay both be members of a first group of nodes. For example, the firstgroup of nodes may operate to cooperatively sense and control anenvironment. The first node may further be a member of a first subnet ofnodes and the communicated information may comprise, among other data,address information of the first node including information identifyingthe first subnet. The second node may be a member of a second subnet ofnodes.

The third node of the present invention may comprise a first side whichis coupled to communicate messages with the first subnet and a secondside which is coupled to communicate messages with the second subnet.The third node may also comprise means for determining whether a messagewas received on the first side or the second side, means for comparingthe address information identifying the first subnet with the subnet ofthe side on which the message was received, and means for controllingretransmission of the message based on such comparison.

In this way, a message received on the first side may be selectivelyretransmitted onto the second subnet only if the message originated fromthe first subnet (and, not if the message originated from the secondsubnet). Importantly, this method reduces unnecessary retransmission ofmessages on the network.

The present invention further reveals method of communicatinginformation in the just described network.

In the present invention, a node on the network may be unconfigured (theterm unconfigured having been better defined above in the discussion ofthe background of the invention). In such a case, the node cannotinclude identifying information in transmitted messages which identifiesits domain/subnet as being the domain/subnet of origin. Therefore, insuch cases where the sending node is unconfigured, it is taught totransmit messages with the domain/subnet fields being set to a firstvalue indicating the node has not yet been assigned to a domain/subnet.A router node, receiving such a message, may replace the first valuewith a second value and then retransmit the message. The second valuepreferably identifies a domain/subnet to which the router node isconfigured. The retransmitted message is then received by a third node.

These and other aspects of the present invention will be apparent to oneof ordinary skill in the art with further reference to the belowDetailed Description of the Preferred Embodiment and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a network as may be implementedutilizing the present invention.

FIG. 2(a) and 2(b) are flow diagrams illustrating prior art methods ofcommunicating messages in a networked system.

FIG. 3 is a diagram illustrating the network of FIG. 1 and furtherillustrating a group of nodes as may be defined in the system of thepresent invention.

FIGS. 4(a) through 4(e) are each flow diagrams illustrating message flowin the system of the present invention.

FIG. 5 is a flow diagram illustrating certain routing rules implementedby the system of the present invention.

FIG. 6 is an overall block diagram of a router node as may be utilizedby the system of the present invention.

FIG. 7 is a block diagram of an integrated circuit chip which may beutilized in a node of the system of the present invention.

FIG. 8 is an illustration of certain fields included in messagestransmitted by nodes of the present invention.

FIG. 9 is an illustration of message flow within a router node of thesystem of the present invention.

For ease of reference, it might be pointed out that reference numeralsin all of the accompanying drawings typically are in the form "drawingnumber" followed by two digits, xx; for example, reference numerals onFIG. 1 may be numbered 1xx; on FIG. 3, reference numerals may benumbered 3xx. In certain cases, a reference numeral may be introduced onone drawing and the same reference numeral may be utilized on otherdrawings to refer to the same item.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

What is described herein is an improved method and apparatus forreducing and preventing the unnecessary retransmission of certain typesof a messages in a networked messaging environment. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be obvious,however, to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to unnecessarily obscure the present invention.

Background references which are applicable to the system of the presentinvention

Perhaps before beginning to describe the preferred embodiment of thepresent invention in detail it is worthwhile to reference U.S. Pat. No.4,918,690 Markkula et al. titled "Network and intelligent cell forproviding sensing, bi-directional communications and control" (referredto herein as the '690 patent) which patent is commonly assigned to theassignee of the present invention and discloses technology relating tonetworked messaging systems. This patent may be useful to anunderstanding of the preferred embodiment of the present invention.

U.S. patent application Ser. No. 07/621,738 Dolin Jr. et al. titled"Configuration Device for Use In a Networked Communication System" filedDec. 3, 1990 (hereinafter the '738 application) also disclosestechnology relating to networked messaging systems. This application maybe useful to an understanding of the preferred embodiment of the presentinvention and, specifically, to an understanding of configuration ofnodes through messages transmitted responsive to activating a servicepin as may be utilized by the system of the present invention. As isstated in the '738 application, when the service pin of a node isactivated, the node transmits a message on the network broadcasting itsnode id and node type.

Now, it is worthwhile to turn to more detailed discussion of the presentinvention and its preferred embodiment.

OVERVIEW OF THE NETWORK OF THE PRESENT INVENTION

The network of the preferred embodiment is of the type which providesfor sensing, control and communication.

For example, the network of the preferred embodiment may be employed ina building such as an office building and provide for such functions assensing temperatures in various locations in the building, communicatingthe sensed temperatures and controlling furnaces and ventilation toselectively heat areas of the building.

It is desirable to provide for installation of a network of the type ofthe preferred embodiment in existing, as well as new, structures and toprovide for such installation at minimal cost while providing formaximum ease of installation. In this regard, nodes of the network ofthe present invention may be coupled with any of several types of media,for example: twisted pair wiring, power lines, radio frequency (RF),etc. In this way, a network may be installed utilizing largely existingcommunication media. This is illustrated, for example, by FIG. 1 whichshows subnet 1 102 of domain 1 131 and subnet 2 103 of domain 2 132.These subnets, subnet 1 102 and subnet 2 103, may be subnets installedwithin a first and a second house. FIG. 1 further illustrates subnet 2101 of domain 1 131 and subnet 1 104 of domain 2 132. These subnets,subnet 2 101 and subnet 1 104, may be subnets associated with a powerline 155.

Thus, it is illustrated in the network of FIG. 1 that nodes such asnodes 110-114, 116-119, 120-124, and 125-128 may be installed onexisting twisted pair wiring and on existing power lines. Although thepreferred embodiment is described with reference to these specificmedia, it is understood that the present invention is essentially mediaindependent.

Certain of the nodes may be installed to function to sense externalfactors, such as the temperature in a room or activity on a media suchas a telephone line; others of these nodes may be installed to controlexternal devices, such as a heater or a telephone answering system.Still others of these nodes may be installed to facilitate communicationbetween nodes in the network. Nodes 114, 116, 119, 122 and 125 ofexamples of a special type of node utilized by the network of thepreferred embodiment to facilitate such communication known as a routernode.

BLOCK DIAGRAM OF THE NODES OF THE PRESENT INVENTION

Each node, with the exception of router nodes, in a network of thepreferred embodiment are implemented utilizing a NEURON® CHIP availablefrom Motorola and Toshiba under license from Echelon Corporation of PaloAlto, Calif. The implementation of router nodes will be discussed ingreater detail below with reference to FIG. 6. Presently there are twomembers of the NEURON CHIP family--the 3120 and the 3150. These twodevices are similar in many respects and, therefore, only the 3150 willbe described in any detail here with reference being made below tocertain differences between the two members of the NEURON CHIP family.It might be noted that inventive aspects of the system described hereinwill perform equally well with either member of the NEURON CHIP familyand, in fact, it will be obvious to those skilled in the art thatinventive aspects of the system described may be accomplished with otherimplementations-such as, for example, an implementation where circuitsof the NEURON CHIP are implemented as discrete or individual componentsor implementations using other integrated circuit modules.

FIG. 7 illustrates in block diagram form a 3150 NEURON CHIP. Importantto many features of the network of the preferred embodiment, each NEURONCHIP includes at time of manufacture, programmed in its EEPROM 701, aunique 48-bit identification number.

The NEURON CHIP is coupled in communication with media 761 throughcontrol 711, clock and timer circuitry 712, and communication port 708.The NEURON CHIP may be connected to an external transceiver for couplingwith other media. The media 761 may be, for example, twisted pair wiring161, twisted pair wiring 162, or power line 155. Of course, media 761may be other types of communication media such as RF, etc. Control 711comprises a reset line and a service pin line. The service pin line isdiscussed in significant detail in the '738 application and it issufficient to state for purposes of an understanding of the presentinvention that activation of the service pin line will cause the node totransmit a broadcast message transmitting its 48-bit node ID and nodetype information.

In addition, the node provides a general purpose I/O port 707 allowingfor communication with various external devices. The I/O port 707comprises 11 I/O pins which may be custom configured in a number ofdifferent configurations including as 11 individually configurabledigital inputs or outputs, as a parallel interface with 8 data and threecontrol lines, or as 8 digital I/O pins and a 3 pin serial interface.Finally, the I/O port comprises two 16-bit counter/timers which may bemultiplexed to certain of the pins to provide for time-domain inputs andoutputs. This configurable pin set up allows the I/O section to becoupled with a large variety of external devices providing for relativeease in providing for communication with, sensing of, and/or control ofsuch devices. Such devices may range from household appliances, tofactory equipment, to automobile accessories. As will be seen, suchdevices may also include another NEURON CHIP, such as utilized by thepreferred configuration of routers.

The node further comprises three separate processors 704-706, a randomaccess memory 702, and an EEPROM 701. The processors 704-706 are usefulfor executing programs such as to provide for communication, sensing andcontrol of information in the network. In the preferred embodiment, twoof the processors are dedicated to protocol processing functions tosupport network communications and the third processor is available tofor applications programs. The EEPROM 701 may be useful for storingcertain data values which, although configurable, are not subject tofrequent changes in value. Each of the processors 704-706, RAM 702,EEPROM 701, control 711, clock 712, I/O port 707, and communication port708 are coupled in communication through internal address bus 710,internal data bus 720 and timing and control lines 730. The NEURON CHIPfurther comprises an external memory interface port 731 which supportsup to 64 Kbytes of external memory.

The 3120 NEURON CHIP (not shown) includes, in addition to the circuitryjust described, 10K bytes of on-chip ROM. However, the 3120 NEURON CHIPdoes not include the external memory interface port 731. Further, the3120 NEURON CHIP includes only 1024 bytes of on-chip RAM instead of the2048 bytes included in the 3150 NEURON CHIP.

DESCRIPTION OF THE ROUTER NODES OF THE PRESENT INVENTION

Router nodes allow for selective communication across two channels. Thetwo channels may exist as two separate physical media, or the channelsmay coexist on the same physical media implemented, for example, as twodiffering carrier frequencies. Routers in the preferred embodiment maybe designed as either learning routers, configurable routers or bridgerouters. Learning routers monitor network traffic to "learn" the networktopology. The learning routers uses the network topology information toselectively route messages between the channels. Bridge routers simplyforward all packets received on one channel to the other channel.Configurable routers utilize routing tables (such as shown withreference to FIG. 6 as Tables 611 and 612) to selectively pass packetsfor a single domain between the two channels. The selective routingprocess is controlled by routing programs which are programmed into therouter and which implement the routing rules given by the routing table.The routing rules of the preferred embodiment are discussed in greaterdetail below.

Router hardware

FIG. 6 illustrates in block diagram from a router node of the presentinvention. A router node in the system of the preferred embodimentcomprises two halves; a first half preferably comprising a NEURON CHIP 1601 coupled with a transceiver 605 and a second half preferablycomprising a NEURON CHIP 2 602 coupled with a transceiver 606. Ofcourse, in alternative embodiments, devices other than NEURON CHIPS maybe used. Therefore, in the remaining description, NEURON CHIP 1 601 willbe referred to simply as chip 1 601 and NEURON CHIP 2 602 will bereferred to simply as chip 2 602.

Chip 1 601 is coupled in communication with chip 2 602 over lines 604allowing for communication between the two halves of the router.

In the preferred embodiment, each of chips 601 and 602 are implementedutilizing 3150 NEURON CHIPs and are coupled in communication utilizingtheir respective 11 I/O pins 741 (which pins are represented on FIG. 6with lines 604). The chips (chip 1 601 and chip 2 602) are configured toallow eight bit parallel communication between the two devices acrossthe I/O interface.

The chips 601 and 602 are each further coupled in communication withtransceivers 605 and 606, respectively, through coupling of theirrespective communication ports 708, control circuitry 711, andclock/timers 712. The transceivers are each coupled with respectivemedia, media 621 and 622. The media 621 and 622 may be, for example asillustrated by node 114, twisted pair 161 on one side and radiofrequency on the other side. Of course, other combinations of media maybe implemented without departure from the teachings of the presentinvention.

One half of the router is defined as a master half and the other half ofthe router is defined as the slave half. This designation of amaster/slave relationship is implemented in the preferred embodiment tosupport the parallel interface between the two halves.

Message Packet Management

Each of the three processors on each half of a router node isresponsible for one primary function (similar to the implementation ofdivision of responsibility between processors in other nodes of thepreferred embodiment). In specific, one processor is designated tosupport the MAC layer functionality of the network of the preferredembodiment (referred to as the MAC processor); a second processor isresponsible for network management functions (referred to as the NETprocessor). This processor also is responsible for routing decisions andfor passing packets to the third processor. The third processor(referred to as the IFC processor) is responsible for transferring andreceiving data across the parallel bus (thus, this third processor isthe processor discussed above responsible for executing applicationprograms-in this case the application program being the programresponsible for communication between the two halves of the router).

It is noted that once received by one half of a router, a message packetis stored in a packet buffer area until it is again retransmitted(either across the parallel interface or onto the media 761). Forexample, when the third processor receives a packet across the parallelinterface (on internal bus 720), the packet is stored in a packet bufferarea in RAM 702. The first processor may then access the packet in thebuffer area and cause it to be transmitted across the internal bus ontothe media 761 through communication port 708. Conversely, the messagemay be received through the communication port 708 and be processed bythe first processor and placed in the packet buffers for forwardingacross the parallel interface to the other half of the router.

In order to facilitate this concept of passing responsibility of amessage packet from one processor to another, a concept of packetownership is adhered to in the system of the preferred embodiment. Thisconcept is better illustrated with reference to FIG. 9. When a packet isreceived by a router on one side (referred to in FIG. 9 as the receiveside 921) from media 621, the packet is initially considered to be ownedand controlled by the MAC processor 901. The MAC processor processes themessage by providing for typical MAC layer functions (the term MAC layeror Medium Access Control layer and the functions carried out by such alayer are well-known to one of ordinary skill and it is not necessary todetail these functions here) and by placing the message in a packetbuffer in RAM 702.

Once the message is placed into the packet buffer, owneship istransferred to the NET processor 902. The NET processor 902 thendetermines whether the message should be processed by the node itself(certain messages, such as network management messages, may be intendedfor processing by the node itself rather than being intended to beforwarded), whether the message should be forwarded to the other side ofthe node, or whether the message should be dropped. The decision onwhether the message should be processed by the node itself can be madebased on whether the message is addressed to the router itself. If themessage is addressed to the router itself, the message is then processedby the router, otherwise, the message is either forwarded or dropped.The decision on whether the message should be forwarded to the otherside of the node or whether the message should be dropped is made basedon the node's routing rules which are discussed in greater detail below.

If the message is to be forwarded, ownership is passed to the IFCprocessor 903 which prepares the message for transfer over the parallelinterface 604 and then transfers the message. The message is thendeleted from the packet buffer on the receive side 921.

The message is then received on the transmit side 922 of the routerunder control of the transmit side's IFC processor 904. The IFCprocessor 904 then places the message in a packet buffer in the transmitside's RAM and passes ownership to MAC processor 905. The MAC processor905 then transfers the message over the communication port 708 ontomedia 622 and the message is deleted from the packet buffer.

GROUPS

Nodes in the network of the preferred embodiment are organized throughinstallation procedures into groups-where a group is defined below inTable I as "a set of nodes which work together to perform a commonfunction." Thus, FIG. 3 illustrates the network of FIG. 1, but adds theconcept of a group, Group 1 301, which comprises two nodes--node 110 andnode 118. In the illustrated example, both node 110 and 118 areorganized within a single domain, domain 1 131; however, these two nodesare located on separate channels with node 110 being coupled tocommunicated on twisted pair wiring 161 and node 118 being coupled tocommunicate on power line 155. Thus, in order for the nodes 110 and 118to communicate with each other (i.e., to communicate between members oftheir group, Group 1 301), messages must be passed through interveningrouters.

For example, node 110 may communicate a message onto twisted pair media161. The message may comprise information illustrated by FIG. 8 whichincludes source address information (source domain 801, source subnet802, and source Node ID 803), destination address information 804,message type information 805 and other message message data 806.Importantly, as is now seen, the message includes address informationfor the source of the message as well as address information for theintended destination(s) of the message.

The address information for the intended destination(s) of the messagewill vary from message to message and will preferably comprise one offive address formats. These five address formats are described ingreater detail with reference to Table III and allow routing to variousdestinations as shown in the table. When sending a group message, asillustrated by the present example, destination address format 4 isutilized to specify the domain id and group. The domain id in theexemplary message is specified as domain 1 and the group id as group 1.

The message is received by router node 114 on its first side (the sidecoupled with media 161) and router node 114 may then retransmit themessage on its second side using radio transmission. The message is thenreceived by node 119 on its first side (shown as coupled a radiofrequency receptor/transmitter) and is retransmitted on node 119'ssecond side onto power line 155. The message may then be received frommedia 155 by its intended recipient, node 118. Of course, thiscommunication process deserves significantly greater discussion in orderto allow for an appreciation of the present invention. This discussionwill be facilitated by with reference to FIGS. 4(a)-(e).

REPRESENTATIVE TRANSMISSION OF A MESSAGE IN THE NETWORK OF THE PRESENTINVENTION

FIGS. 4(a)-(e) illustrates exemplary message transmissions in the systemof the preferred embodiment.

Transmission of the group message onto media 161

Initially, node 110 may transmit a group message onto media 161. As hasbeen just discussed, the message comprises source address information inaddition to the destination address information (such as preferablydescribed in connection with FIG. 8), block 401. This source addressinformation includes information identifying node 110 as a being amember of subnet 1 102, and further identifying node 110 as being amember of domain 1 131.

The message is received by each of the other nodes coupled with media161 (e.g., nodes 111-113 and router node 114).

When the packet is received by nodes 111-113, the network processingprotocol programs executing on a processor in each of those nodesdetermines that the message is not intended for the respective node asit is a group message and the node is not a member of the specifiedgroup. The message is, therefore, ignored or dropped, block 411.

As was stated, the message is also received by router node 114 on theside of router node 114 coupled with media 161, block 402. It hasalready been explained in some detail above how the router receives andprocesses the message packet and allows the message packet to beretransmitted on its second side. To add to the description of theretransmission process, it is briefly stated here that the decision toretransmit the message is carried out in accordance with the routingrules implemented in the system of the preferred embodiment. Thoserules, for group addressed messages, generally call for first examiningthe group forwarding tables (discussed below) to determine if the groupmessage should be forwarded and then examining the source subnet field802 of the message to determine if the source subnet is on the receiveor transmit side of the router (see FIG. 9 for a description of thereceive and transmit sides of the router), blo If the source subnet ison the receive side of the router, the message is retransmitted. If thesource subnet is on the transmit side of the router, the message is notretransmitted. By not retransmitting messages where the source subnet ison the transmit side of the router, unnecessary retransmission ofmessages is avoided as it can be assumed that such messages havepreviously been transmitted on the subnet on that side of the router.

(It is noted that, in fact, in the implementation of the preferredembodiment, both the source subnet field 802 and the source domain field801 are examined to determine if the message should be forwarded. It isimportant in the system of the preferred embodiment to examine both thesource subnet field 802 and source domain field 801 because subnetnumbers may be duplicated from domain to domain. There are also otherrouting rules which are followed by the system of the preferredembodiment. For sake of simplifying the example given here, the systemwill be described as examining the source subnet field 802 in making therouting decision-however, it is understood that, in fact, the routingrules explained in greater detail below are followed.)

Retransmission of the group message onto power line 155 by router node119

If the message is to be retransmitted (as determined by the routingrules which are expressed in routing table, such as table 611 or 612stored in the on-board EEPROM 701), block 404, it is retransmitted onthe second side, block 405. In the illustrated example, thisretransmission is done using radio frequency transmission from thesecond side of node 114. Of course, the radio signals are intended to bereceived by router node 119 for retransmission on power line media 155so that the message will eventually be received by node 118. Processingof the message by router node 119 will be discussed below.

However, before discussing processing by router node 119, it is pointedout that the message may also be received by router node 116 and routernodes 122 and 125, blocks 407 and 408, respectively. Processing by nodes122 and 125 will be discussed first as that is the relatively simplecase; this discussion will be followed by a discussion of processing bynode 119, and finally by a discussion of processing by node 116.

It is pointed out that according to the routing rules of the preferredembodiment, if the message had been originated by a node with an addressof source subnet 1, the message would not have been retransmitted byrouter node 114, block 409.

Processing by node 122--FIG. 4(d)

FIG. 4(d) details the process followed in the case of the message beingreceived by nodes 122 or 125. In the following discussion, forsimplicity, only node 122 will be specifically discussed with theunderstanding that processing by node 125 is similar.

Node 122 examines the source subnet address information to determine ifthe message should be retransmitted on its transmit side, block 471. Inthe case of the present example, the routing rules provide forretransmission of the message because it cannot be determined by node122 whether any member of the group specified by the group message arecoupled with a twisted pair wiring 162. Therefore, a determination ismade that the message should be retransmitted, block 472, and node 122retransmits the message onto media 162, block 473. The message is thenreceived by each of nodes 120-124 and, as these nodes are not members ofgroup 1, the message is ignored, block 475.

Of course, if the message had been originated by a node with an addressof source subnet 2, the message would not have been retransmitted byrouter node 122, block 482. It is also understood that, in accordancewith the routing rules of the preferred embodiment, because node 122 isnot a member of domain 1 131, in the system of the preferred embodiment,node 122 would not, in fact, retransmit the message. Similarly, in thesystem of the preferred embodiment, node 125 would not retransmit themessage because it is also not a member of domain 1 131.

Processing by node 119--FIG. 4(b)

Initially, when node 119 receives the message it examines the sourcesubnet field 802 to determine if the message should be retransmitted,block 421. The apparatus and methods for carrying out this examinationhave already been well-discussed. If the message should beretransmitted, block 422, node 119 retransmits the message and themessage is received by node 118, block 424 where the message isprocessed, block 431.

The message is also received by nodes 117 and 126-128. Each of nodes 117and 126-128 ignore the message because none of these nodes are membersof group 1. In addition, in the system of the preferred embodiment,nodes 126-128, as well as router node 125 will ignore the messagebecause these nodes are not members of domain 1 131.

Finally, the message is also received by router node 116. Node 116follows its routing rules to determine whether the message should beretransmitted. In the particular case, the message will, likely, not beretransmitted because it will be determined that the source subnet lieson the destination side of the router. These rules are discussed ingreater detail below.

It should be noted that if the source subnet field 802 had indicated thesource subnet was subnet 2, according to the routing rules thus fardiscussed, the message would not have been retransmitted by node 119.

Processing by node 116--FIG. 4(c)

When router node 116 first receives a message, it examines the sourcesubnet field 802 to determine if the message should be retransmitted. Ashas been seen, node 116 may receive the message on both of its twosides-likely first receiving the message when transmitted in radio waveform from node 114 on a first of its two sides and, then again receivingthe message when it is retransmitted onto the power line media 155 bynode 119 on a second of its two sides. In the case of the message beingreceived in radio wave form from node 114, node 116 initially examinesthe source subnet information in the message to determine if the messageshould be forwarded.

In this case, the routing rules call for forwarding the message as theoriginating source subnet was on receive side of the router and thedecision is made to retransmit the message, block 442. Therefore, routernode 116 retransmits the message, block 443. When the message isretransmitted, it is received by node 118 and, likely, ignored as aduplicate, block 444. It is also received by nodes 117 and 126-128 whichall ignore the message, block 445. Finally, the message is received byrouter node 119, block 446. Router node 119 processes the message asillustrated in FIG. 4(b) and, in this case, the decision is made not toretransmit the message, block 422.

Now, when the message is again received on router node 116's other sidefrom power line media 155, node 116 again examines the source subnetinformation in the message to determine if the message should beforwarded, block 441. In this case, the determination is made that themessage should not be forwarded, block 442. The message is, therefore,not retransmitted, block 452.

Broadcast Node ID messages--FIG. 4(e)

It has been noted above that the system of the preferred embodimentprovides for the ability of a node to transmit it a message on the mediaresponsive to a stimuli including its unique Node ID. This feature ofthe system of the present invention is often used when configuring nodesof the network in order to obtain a node's Node ID as part of theconfiguration process. However, when a node is unconfigured, it has notyet been assigned a subnet number or domain. Therefore, the sourcedomain field 801 and source subnet field 802 are set to a valueindicating these fields are currently unassigned. In the preferredembodiment, the value used is zero; but it is pointed out that inalternative systems other values may be used without departure from thespirit and scope of the present invention.

It can be appreciated that in the system which has been described abovewhich determines routing requirements at least in part based on thesource subnet and source domain fields 801 and 802, transmitting amessage having these fields set to "unassigned" will lead todifficulties. Therefore, another aspect of the present invention isdescribed with reference to FIG. 4(e) which illustrates the process forbroadcasting a Node ID message where the source node is unconfigured. Inthe example, node 110 is assumed to be an unconfigured node.

Node 110 initially broadcasts a Node ID message message onto media 161responsive to a stimuli, as has been described. The source subnet field802 and source domain field 801 are both set to a value indicating thesefields are unassigned; in the preferred case, these fields are each setto zero, block 481.

Each of nodes 111, 112 and 113 receive the Node ID message and processor ignore depending on their particular programming, block 482.

Router node 114 also receives the Node ID message on a first side (inthis case, the side coupled with media 161). Router node 114 thenreplaces the contents of the source domain field 801 with its own domainvalue (i.e., in the example, the source domain field 801 will now be setto "Domain 1") and router node 114 replaces the contents of the sourcesubnet field 802 with its own subnet value (i.e., in the example, thesource subnet field 802 will be set to "Subnet 1"), block 483. Therouting of the message then follows the regular routing rules;therefore, node 114 then retransmits the message from its second side,block 484.

The message, retransmitted from node 114's second side, is thenprocessed by the receiving nodes in the manner previously described inconnection with FIG. 4(e).

ROUTING RULES Up to two domains defined per router

Before continuing, it is worthwhile to point out that in the preferredembodiment of the present invention, each router may be configured to bea member of up to two separate domains. This allows greater flexibilityin configuring networks of the preferred embodiment. The routing rules,described below, take into account this capability.

In the preferred embodiment of the present invention, as was describedearlier in connection with FIG. 6, each router node includes, in each ofits halves, a routing table 611 and 612. In fact, the preferredembodiment includes three tables in each half--a first routing tablehaving therein subnet information for a first domain, a second routingtable having therein subnet information (referred to collectively withthe first routing table as the "subnet routing table") for a seconddomain, and a third routing table having group information (the "grouprouting table").

Subnet routing tables

The subnet routing tables are used for routing messages in which thedestination is referred to by a subnet number (i.e., formats 2 and 3 ofTable III, below). The preferred embodiment of the present inventionallows up to 255 subnets per domain. Each subnet routing table containsa flag for each of the 255 subnets in the domain associated with thetable and serviced by the router. The flag indicates if messagesdestined for that subnet are to be forwarded by the router (if the flagis set in the preferred embodiment, the message is to be forwarded).

Group routing table

The group routing table is used for routing messages in which thedestination nodes are referred to by a group number (i.e., format 4 ofTable III, below). The preferred embodiment of the present inventionallows up to 256 groups per domain. The group routing table contains aflag for each of the 256 groups in the domain which indicates ifmessages destined for that group are to be forwarded by the router (ifthe flag is set in the preferred embodiment, the message is to beforwarded).

Addressing modes

Table II, below, illustrates the various addressing modes of the systemof the preferred embodiment and the routing rules implemented tofacilitate routing of messages using those addressing modes. Theaddressing mode used by a message is defined in the message by itsdestination address information 804.

Address mode 1 (sometimes referred to as broadcast addressing) allowsrouting to all nodes in a particular domain. Routers will forwardmessages using this address mode if the router is a member of thespecified destination domain and if the other routing rules of thesystem of the preferred embodiment are met. These other routing ruleswill be discussed in greater detail below. Optionally, a destinationsubnet may be specified. In this case, the router must be a member ofthe destination domain and destination subnet in order to forward therouter. If a router receives a message destined for a domain/subnetother than the domain/subnet serviced by the router, the message is notretransmitted.

Address mode 2 (sometimes referred to as unicast addressing) requiresthat a check be made of the subnet table of the receive side of therouter to determine if the forward flag for the destination subnetspecified in the message is set. If the forward flag is set, the messageis intended to be forwarded. However, in accordance with one inventiveaspect of the system of described herein, before forwarding the message,a check is made to determine if the source subnet is on the transmitside of the router. This will be discussed in greater detail below inconnection with FIG. 5. In addition to checking the subnet table, acheck is made to determine if the destination domain/subnet matches thedomain/subnet of the router.

Address mode 3 (sometimes referred to as multicast addressing) requiresthat a check be made of the group table of the receive side of therouter. If the group table forward flag for the group specified by thedestination address indicates the message is to be forwarded, themessage is forwarded if the source subnet is not on the transmit side ofthe router. Again, the source subnet is checked against the subnet tableto determine if the source subnet is on the destination side of therouter and the destination domain is checked to determine if the domainof the router matches.

Finally, address mode 4 (sometimes referred to as the unique ID mode)illustrates an addressing mode in which the unique 48-bit id of thedestination node is specified. After determining whether the sourcesubnet lies on the destination side of the router, and otherwisefollowing the routing rules described herein, messages using thisaddressing mode are forwarded.

Check if destination domain matches the domain of the router

It is now time to turn to FIG. 5 which is a flow diagram illustratingthe routing rules implemented by routers in the preferred embodiment ofthe present invention. As has been discussed above, in the first threeaddressing modes, a check is done to determine if the destination domain(and, if specified, the destination subnet) match the domain/subnet ofthe router, block 501. It is again noted that each router in the systemmay be configured to be a member of up to two domains. Therefore, thischeck is performed against each of these domains.

The system of the preferred embodiment allows nodes to send broadcastmessages without specifying a destination domain. If the message is abroadcast message and the destination domain and source subnet arespecified as a special value (in the preferred embodiment, the specialvalue is represented as a zero length value in the destination domainfield and a zero in the source subnet field). If the special value isnot present in these fields, the packet is dropped by the router, block505. Otherwise, the router substitutes its own domain information forthe special value in the destination domain field and substitutes itsown subnet for the source subnet and forwards the packet, block 511. Inthe event that the router is configured as a member of two domains, thepacket is forwarded twice--the first time specifying the first domain ofwhich the router is a member and the second time specifying the seconddomain.

Check if the source subnet is undefined

Importantly, as has been discussed, in the system of the preferredembodiment, a node may be allowed to transmit messages onto the networkwithout having yet been configured to be a member of a particularsubnet. Therefore, when a message is received which is addressed to oneof the domains serviced by the router, a check is done to determine ifthe source subnet is defined in the message (unconfigured nodes transmitmessages with the source subnet field set to zero), block 502.

In the case of messages which are transmitted with the source subnet setto zero, a check is done to determine if the domain length is also zeroand if the message is a broadcast message, block 503. If it is,processing continues as described above in connection with block 504.This test is necessary because routers may be configured as beingmembers of domain length zero.

As one important aspect of the present invention, assuming the domainlength is not zero, the router sets the source subnet field 802 to itsown subnet value, block 506, and sets the source domain field to its owndomain. This step is important in prevention of unnecessary rerouting ofmessages in the system of the preferred embodiment and, further, allowsnodes to initially be installed in an unconfigured state and allows suchunconfigured nodes to communicate on the network. In messagestransmitted by unconfigured nodes, the source subnet field 802 andsource domain field 801 are both set to an unconfigured value. In thepreferred embodiment, this value is zero. In the system of the preferredembodiment, substitution of the router's address information for thesource address information (as accomplished by block 506) is only donewhen the message was originated by an unconfigured router and if themessage was received directly from the origin node (because if themessage had been previously received an retransmitted by another routernode, that node would have done the substitution).

Group message forwarding algorithm

Message retransmission depends on the type of addressing mode of themessage. Beginning with group addressing, block 507, a check is made ofthe group table to determine if messages destined for the group are tobe forwarded by the router, block 512. This is accomplished by checkingthe group table on the receive side of the router to determine if theforward flag for the destination group address in the message is set. Ifthe flag is not set, the message is not forwarded by the router and thepacket is dropped, block 519.

If the flag is set, as another important aspect of the presentinvention, a check is made to determine if the source subnet is on thedestination side of the router, block 517. This is preferablyaccomplished by checking the subnet forward flag in the subnet routingtable for the specified domain on the receive side of the router. If theflag is not set, the source subnet is determined to not be on thedestination side of the router and the packet is forwarded, block 518.If the flag is set, source subnet is determined to be on destinationside of the router and the packet is dropped, block 519. This aspect ofthe present invention significantly reduces the possibility of infiniteloops being created when routing messages in the network of the presentinvention and generally reduces the number of unnecessaryretransmissions of messages in the system of the present invention.

Unicast message forwarding algorithm

Processing for messages using subnet addressing, block 512, is similarto processing for messages using group addressing. However, instead ofchecking the group forward flag, a check is made of the subnet forwardflag for the destination subnet in the subnet routing table, block 515.If the forward flag for the destination subnet is set, then processingcontinues as has been described in connection with the description ofblock 517 above. Otherwise, the message is not forwarded by the routerand the packet is dropped.

Broadcast message /Unique ID forwarding algorithm

Routing of messages using broadcast messaging or unique ID messaging ishandled similarly, block 513. If the destination subnet is specified aszero, block 516, the processing continues as described above inconnection with block 518. Otherwise, if a destination subnet isspecified, processing continues as specified above in connection withblock 515.

Thus, what has been described is an improved method of routing messagesin a networked system in which method there is achieved reducedunnecessary retransmission of messages.

                  TABLE I                                                         ______________________________________                                        GENERAL DEFINITIONS                                                           ______________________________________                                        The following definitions are generally applicable to terms used              in this specification:                                                        Addressing -                                                                           The present invention provides for a hierarchical                             address structure and supports three basic address-                           ing modes: (1) (Domain, Subnet, Node number);                                 (2) (Domain, Subnet, Node.sub.-- id); and (3) (Domain,                        Group).                                                              Channel -                                                                              Nodes within a network are coupled together on                                communications media, for example, a power line                               or telephone line. In a typical network, there may                            be one or more channels. Communication between                                channels in a network is accomplished by routing                              messages through a bridge or router node. There                               may be a one-to-many relationship between                                     channels and domains and a one-to-many                                        relationship between domains and channels.                           Domain:  The term "domain" is used to describe a virtual                               network wherein all communication, as supported                               by the network of the present invention, must be                              within a single domain. Any required inter-domain                             communication must be facilitated by application                              level gateways.                                                      Domain   In the preferred embodiment, domains are                             addresses:                                                                             identified with 48-bit domain identifiers. However,                           in certain applications the size of the domain field                          may vary.                                                            Group:   A group is a set of nodes which work together to                              perform a common function. In the preferred                                   embodiment, groups are identified with an 8-bit                               group identification number. A single domain may                              contain up to 256 groups.                                            Node:    A node is an intelligent, programmable element                                providing remote control, sensing, and/or                                     communications, that when interconnected with                                 other like elements forms a communications,                                   control and/or sensing network. Nodes are                                     named with Node ids (see below). Nodes may                                    be addressed as a part of a domain and subnet                                 using a node number. The node number in the                                   preferred embodiment is 7 bits. Multiple                                      nodes may be addressed using a group id. The                                  group id in the preferred embodiment is 8 bits.                      Node id: Nodes in the present invention are assigned a                                 unique identification number at the time of                                   manufacture. The identification number is preferably                          48-bits long. This 48-bit identification number                               does not change during the lifetime of node. As                               is appreciated, the assignment of a unique                                    identification to each individual node allows                                 for numerous advantages. This 48-bit identification                           number may be referred to as the Node id.                            Subnet - In the preferred embodiment, a subnet is a subset                             of a domain containing from 0 to 127 nodes. In the                            preferred embodiment, subnets are identified with                             an 8-bit subnet identification number. A single                               domain may contain up to 255 subnets.                                ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        FORWARDING RULES                                                              The following destination address formats are forwarded by                    routers of the system of the preferred according to the stated                forwarding rules:                                                             ADDRESS  ADDRESS                                                              MODE #   FORMAT    FORWARDING RULES                                           ______________________________________                                        1 - Broadcast                                                                          Domain    If the source address information = 0,                              (and,     first modify the source address                                     optionally                                                                              information; then, if the destina-                                  subnet)   tion domain matches a domain of                                               which the router node is member,                                              forward (if destination subnet is                                             specified, router node must be a                                              member of the specified subnet                                                also.)                                                     2 - Unicast                                                                            Domain    If source address information = 0,                                  Subnet    then modify the source address                                      Node      information; then, if destina-                                                tion domain matches perform a                                                 subnet table check                                         3 - Multicast                                                                          Domain    If source address information = 0,                                  Group     then modify the source address                                                information; then, if destination                                             domain matches perform a group                                                table check, then forward the                                                 message                                                    4 - Unique                                                                             Unique    If source address information =  0,                          ID     48-bit ID then modify the source address                                                information; then forward the                                                 message                                                    ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        ADDRESS FORMATS                                                               The following four generalized address formats are utilized                   for transmission of messages in the system of the                             preferred embodiment:                                                                   ADDRESS FORMAT                                                      FORMAT #/ (Destination address                                                Type      information)    DESTINATION                                         ______________________________________                                        1 - Broadcast                                                                           Domain (and,    All nodes in the                                              optionally, subnet)                                                                           specified domain                                                              (if subnet information                                                        is included, only nodes                                                       in the specified                                                              destination domain/                                                           subnet.                                             2 - Unicast                                                                             Domain          The specified node                                            Subnet Node     within the indicated                                                          subnet and domain                                   3 - Multicast                                                                           Domain Group    All nodes within the                                                          specified group                                     4 - Unique ID                                                                           Unique 48-bit ID                                                                              The specified node                                  ______________________________________                                    

What is claimed is:
 1. A network for communicating information, saidnetwork comprising:(a) a first node for communicating information, saidfirst node being a member of a first subnet of nodes, said communicatedinformation comprising address information of said first node, saidaddress information including information identifying said first subnetof nodes; (b) a second node for receiving said communicated information,said second node being a member of a second subnet of nodes; (c) a thirdfor receiving said communicated information from said first node and forrouting said communicated information to said second node, said thirdnode having:(i) a first side coupled to receive communicated informationfrom said first subnet of nodes, (ii) a second side coupled tocommunicate communicated information to said second subnet of nodes,(iii) determining means for determining whether or not communicatedinformation received on said first side was originated by a node on saidsecond side, and (v) control means for controlling retransmission ofsaid communicated information, said control means allowingretransmission of said communicated information when said determiningmeans indicates said communicated information was not originated by anode on said second side.
 2. The network as recited by claim 1 whereinsaid communicated information is a group message destined for members ofa first group, said first node and said second node being members ofsaid first group.
 3. The network as recited by claim 1 wherein saiddetermining means accesses a subnet table to determine whether or notcommunicated information received on said first side was originated by anode on said second side.
 4. The network as recited by claim 3 whereinsaid subnet table comprises one entry for each possible subnet in adomain of the third node, one of said entries comprising a flagindicating whether messages for one of said subnets are to be forwardedby said third node.
 5. In a networked system, said networked systemcomprising a first node, a second node and a third node, said first nodebeing a member of a first set of nodes, said second node being a memberof a second set of nodes, said first set of nodes coupled incommunication with said second set of nodes through said third node,said first node capable of transmitting a message to said second node,said message comprising address information of said first node, saidaddress information comprising a first field identifying said first setof nodes, wherein said third node comprises:(i) a first side coupled toreceive said message from said first node; (ii) a second side coupled totransmit said message to said second node, (iii) determining means fordetermining whether or not communicated information received on saidfirst side was originated by a node on said second side; and (iv)control means for controlling retransmission of said message, saidcontrol means disallowing retransmission of said message if saiddetermining means determines that said message was originated by a nodeon said second side.
 6. The network as recited by claim 5 wherein saidcommunicated information is a group message destined for members of afirst group, said first node and said second node being members of saidfirst group.
 7. The network as recited by claim 5 wherein saiddetermination means accesses a subnet table to determine whether or notcommunicated information received on said first side was originated by anode on said second side.
 8. The network as recited by claim 7 whereinsaid subnet table comprises one entry for each possible subnet in adomain of the third node, one of said entries comprising a flagindicating whether messages for one of said subnets are to be forwardedby said third node.
 9. A method for the communicating of information ina network comprising the steps of:(a) communicating information from afirst node onto a media, said first node being a member of a firstsubnet of nodes, said communicated information comprising addressinformation identifying said first subnet; (b) a second node receivingsaid communicated information from said first node, said second nodehaving:(i) a first side coupled to communicate messages to said firstsubnet, (ii) a second side coupled to communicate messages to a secondsubnet, (iii) determining means for determining whether or notcommunicated information received on said first side was originated by anode on said second side, (v) control means for controllingretransmission of said communicated information to a third node, saidcontrol means disallowing retransmission of said message if saiddetermining means determines that said message was originated by a nodeon said second side; and (c) said third node receiving said communicatedinformation when said communicated information is retransmitted, saidthird node being a member of a second subnet of nodes.
 10. The method asrecited by claim 9 wherein said communicated information is a groupmessage destined for members of a first group, said first node and saidthird node being members of said first group.
 11. The network as recitedby claim 9 wherein said determination means accesses a subnet table todetermine whether or not communicated information received on said firstside was originated by a node on said second side.
 12. The network asrecited by claim 11 wherein said subnet table comprises one entry foreach possible subnet in a domain of the third node, one of said entriescomprising a flag indicating whether messages for one of said subnetsare to be forwarded by said third node.
 13. A networked systemcomprising:(a) a first node coupled with a media for transmitting amessage onto said media, said message comprising address information,said address information comprising a subnet field, said subnet fieldrepresenting a value, said first node setting said subnet field to afirst value indicating said first node has not yet been assigned to asubnet; (b) a router node for receiving and retransmitting said message,said router node replacing said first value with a second value; and (c)a third node for receiving said retransmitted message.
 14. The networksystem as recited by claim 13 wherein said address information furthercomprises a domain field, said domain field being set to a third valueby said first node, said third value indicating said first node has notyet been assigned to a domain and wherein said router node furtherreplaces said third value with a fourth value.
 15. The network asrecited by claim 13 wherein said second value is set to a valuecorresponding with said subnet.
 16. The network as recited by claim 13wherein said first value is zero.
 17. The network as recited by claim 14wherein said fourth value is set to a value corresponding with a firstdomain which said router is a member of.
 18. A method for retransmissionof messages in a networked system comprising the steps of:(a) a firstnode transmitting a message onto a media, said message comprisingaddress information, said address information comprising a subnet field,said subnet field representing a value, said first node setting saidsubnet field to a first value indicating said first node has not yetbeen assigned to a subnet; (b) a router node receiving andretransmitting said message, said router node replacing said first valuewith a second value; and (c) a third node for receiving saidretransmitted message.
 19. The method as recited by claim 18 whereinsaid address information further comprises a domain field, said domainfield being set to a third value by said first node, said third valueindicating said first node has not yet been assigned to a domain andwherein said router node further replaces said third value with a fourthvalue.
 20. The method as recited by claim 18 wherein said second valueis set to a value corresponding with said subnet.
 21. The method asrecited by claim 20 wherein said first value is zero.
 22. The method asrecited by claim 19 wherein said fourth value is set to a valuecorresponding with a first domain which said router node is a member of.23. The method as recited by claim 22 wherein said fourth value is setto a value corresponding with a first domain which said router node is amember of.